1. Field of the Invention
The present invention relates to an image signal processing apparatus and an image display each having a function of detecting a black band region included in an image signal, and an image display method performing such a black band detecting process.
2. Description of the Related Art
Image displays such as television receivers (TVs) typically have an image processing function which makes image quality correction to an input image (for example, functions such as luminance or contrast control, and contour correction). Such an image processing function is performed by acquiring, for example, the average peak level (APL) of an input image signal or the histogram distribution of a luminance level, and is effectively applied, because gradation is improved by preventing an image from appearing too dark or preventing poor reproduction of black.
Among image signals from DVDs containing Cinemascope size images or image signals transmitted from broadcast stations, there are a signal called a letterbox including black band regions above and below an image region, and a signal called a side panel including black band regions on the right and the left of an image region. When the above-described image processing is performed on such an image signal including the black band regions, the image processing is performed also on the black band regions which are independent of the contents of the image region, so image quality is not appropriately corrected, and the effect of the image processing is reduced.
Therefore, to effectively detect a black band region included in an input image signal in such a manner, various methods are proposed (for example, refer to Japanese Patent No. 3429842 and Japanese Unexamined Patent Application Publication Nos. H05-27736 and 2005-203933.